Flexible planar heating unit adapted for mounting on complex curved surfaces

ABSTRACT

A sheetlike, flexible heating unit of the semiconductive type having a central body portion provided with bus bar means and spaced protruding arms each having a bus bar at the tip thereof, said unit being adapted to be fitted tightly against an underlying curved surface of nonsimple configuration without engendering any substantial folding or overlapping of the heating unit.

United States Patent Inventor Emil J. Luger, Jr.

San Francisco, Calif. Appl, No. 837,638 1 Filed June 30, 1969 Patented Jan. 26, 1971 Assignee Delta Control Inc.

San Francisco, Calif. a corporation of California FLEXIBLE PLANAR HEATING UNIT ADAPTED FOR MOUNTING ON COMPLEX CURVED SURFACES 3 Claims, 10 Drawing Figs.

us. c1 219/528, 219/202,219/211,219/217,219/243,219/249, 219/544, 338/21 1, 338/309 1m. (:1 H05b 3/36 Field 61 Search 2 l9/528- 156 References Cited UNITED STATES PATENTS 2,277,772 3/1942 Marick 219/211 2,473,183 6/1949 Watson 219 543 2,688,679 9 1954 Schleuning 338 309X 2,878,357 3 1959 Thomsonetal. 219 203x 3,344,385 9/1967 Bartosetal 338/2l2 3,379,858 4 1968 Peters 219/522 3,397,302 8/1968 HOSfOl'd 1 219 528 3,400,254 9 1968 Takemori 219 549 3,478,191 11/1969 Johnsonetal. 219/543x Primary Examiner-Volodymyr Y. Mayewsky Attorney-Gregg & Hendricson ABSTRACT: A sheetlike, flexible heating unit of the semiconductive type having a central body portion provided with bus bar means and spaced protruding arms each having a bus bar at the tip thereof, said unit being adapted to be fitted tightly against an underlying curved surface of nonsimple configuration without engendering any substantial folding or overlapping of the heating unit.

BACKGROUND OF THE INVENTION Planar, flexible heating units of the type with which this invention is concerned are laminated structures having an inner, semiconductive core which is bonded between electrically insulating plastic face panels. Heat is generated as electrical current is passed between spaced bus bars provided on said inner core. In the past, units of this character have possessed a rectangular or other outline of regular configuration which adapted the heater to be pressed tightly against flat surfaces or those of essentially simple curvature. On the other hand, in fitting such heater shapes to spheres and other articles such as airplane wings having curved surfaces of compound or complex configuration, it is necessary to overlap certain elements of the heater (thereby providing localized hot spots) or to leave an upstanding fold or crease in the body of the heater which gives rise to an area of relatively poor heat transfer. It is an object of the present invention to overcome these deficiencies by providing a planar heating element so shaped that it may be secured against underlying surfaces of nonsimple curvature without being creased or overlapped.

SUMMARY OF THE INVENTION The present invention is based on the provision of a flexible heating unit of the semiconductive type having a relatively thin, planar configuration which, by virtue of its having a cen tral body portion from which extend spaced, generally parallel arms, is adapted to be tightly fitted without creasing or overlapping against underlying surfaces having a spherical or other curvature of complex configuration. More specifically, the heating unit is one comprising an inner, semiconductive core layer bearing spaced bus bars which is laminated between electrically insulating face panels which are bound to opposed sides of the core layer and which cover the bus bars. These panels extend outwardly of the core layer about substantially the entire periphery of the unit and are bound to one another in these marginal areas. In outline, the heating unit presents a principal body portion having a core layer provided along its length with bus bar means and, projecting-from principal body portion in directions generally perpendicular to said bus bar means, a plurality of spaced, generally parallel arms each having a core layer which is integral with that in the principal body portion and which is provided with a bus bar adjacent its outer extremity. In operation, current supplied the first mentioned bus bar means passes through the core layer of the principal body portion and then in parallel flow through the core layer of the projecting arms to the respective bus bars provided at the arm extremities, thereby heating the unit. If desired, the central body portion of the unit may be provided with two or more bus bars, insulated from one another, each of which acts to receive current and then to pass the same through a given series of extending arms to their terminal bus bars.

The projecting arms of the unit, being spaced in some mea' sure from their root to their terminal portions, have a certain amount of flexibility in a lateral plane and thus permit the heating unit to assume the shape of the underlying article without engendering any substantial folding, creasing or overlapping of the respective central or arm portions of the unit.

As indicated above, the heating unit of the present invention incorporates a semiconductive planar or sheetlike core element having characteristics which enable it to conduct electrical current passed therethrough between spaced bus bars with resultant production of heat. A preferred material of this type comprises a polyimide material incorporating finely divided carbon particles, as described in U. S. Pat. No. 3,359,525 to Hubbuch, though other useful semiconductive materials of a flexible character are also taught in the art as,

for example, in U. S. Pat. No. 2,952,76l to Smith-Johannsen. In fabricating the heater unit, the semiconductive core layer is first cut to the desired outline leaving a sufficient amount of space between the margins of the extending arms so as to permit the later-applied insulating panels to contact one another along the arm margins, while leaving some space between the adjacent insulated arm margins. The bus bars are then placed on the unit and secured thereto in any convenient fashion as by the use of adhesives, or the like, said bus bars being fabricated of a conductive metal such as aluminum or copper in foil, paint, powder or other conductive form. The core layer, with its attached bus bars, is then sandwiched between electrically insulating panels of a material such as nylon, Nomex, polyester, Teflon or the like. The latter materials are then firmly bonded (over the bus bars) to a semiconductive core layer, using adhesives where necessary, by the application of heat and pressure. The insulating panels employed may, if desired, be precut so as to generally correspond with the cutout shape of the core layer, allowing some extension at the edges, or they can be applied as rectangular sheets large enough to cover the entire core structure. The article is then laminated in such a fashion as to bond the insulating panels to I the underlying core layer as well as to one another in the areas where no core layer intervenes. Thereafter, the webs of bonded insulation panel material between the arms of the unit can be trimmed out leaving a heating unit of the desired shape. Electrical leads, insulated as required, can then be applied to the unit (e.g., by piercing the insulation layer) in such fashion as to make good permanent connections with the bus bars or, alternatively, the heating unit can be glued or otherwise applied to the curved surface of the article to be heated, with the leads then being attached to the bus bars. Reference is hereby made to the foregoing patents fora more complete disclosure of methods and materials to be employed in preparing flexible heating units of the semiconductive type as employed in a practice of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The objects and advantages of this invention will become apparent from the description that follows when read in conjunction with the accompanying drawings wherein:

FIG. I is an exploded view of a metal unit having an end section of compound curvature against which is fitted a heating unit embodying features of this invention;

FIG. 2 is a view similar to that of FIG. I, but with the structure being rotated approximately to better present for view the surface to be covered by the heating unit;

FIG. 3 is a plan view of the planar heating unit which, in FIG. 1, is shown in a curved position;

FIG. 4 is an end view of the heating unit taken along the line- 4-4 of FIG. 3;

FIG. 5 is a view similar to that of FIG. 3, but further showing the electrical circuitry by which current is supplied to the various bus bars of the unit;

FIG. 6 is a sectional view, to an enlarged scale, taken along the line 6-6 of FIG. 5;

FIG. 7 is a plan view of another embodiment of a heating unit embodying features of this invention;

FIG. 8 is an exploded view of the elements of the heating unit of FIG. 7 prior to laminating the structure;

FIG. 9 is a sectional view, to an enlarged scale, taken along the line 9-9 of FIG. 7; and

FIG. 10 is a schematic view showing the flow of electrical current through the elements of the heating unit of FIG. 7 as the latter is placed against the surface of a spherical article.

Referring now more particularly to FIGS. 1 and 2 of the drawings, there is shown a solid metal member generally indicated at 10 having a forward wall 11 and an end wall 12, the surfaces of which are to be heated by the application thereto of flexible, planar heating units of appropriate shape. End 12 presents a surface of compound curvature, and to this surface is applied a heating unit as generally indicated at 15, the latter unit being secured to the underlying metal surface by means of a suitable adhesive composition which sets up in the conventional fashion by application of heat and pressure. As indicated in FIGS. 3 through 6, heater unit when lying unfolded in a position of rest, has a principal body portion 16 provided with a bus are bar 17 extending the length thereof, together with a series of arms 18, 19, 20 and 21 which project from said body portion in a direction generally perpendicular to bus bar 17. These arms are provided at their terminal portions with individual bus bars 22, 23, 24 and 25. Due to the presence of these discrete arm portions (as well as to the fact that the material thereof is capable of being flexed to at least a limited degree), the heater unit is enabled to assume the position shown in FIGS. 1 and 2 wherein the arms are spread further apart than in the position of rest, thereby permitting the unit to accommodate itself in a generally smooth fashion to the underlying metal surface.

As indicated in FIG. 6, heater unit 15 is composed of a semiconductive core section 30 which is laminated between electrically insulating side panels 31 and 32. In the areas between the respective arms of the heater unit, as well as about the remaining margins of the unit, the panels 31 and 32 are fused to one another as shown, for example, at 33 (periphery) and 34 (between the arms) where the core layer 30 is not present to form an intervening layer. Moreover, the fused portions 34 between the respective arm of the heater -unit are slit as shown at 35 so as to effect separation of the arms 18, 19, 20 and 21 from one another for the desired length.

As seen particularly in FIG. 5, the heater unit 15 is provided with an electrical lead 40 which is secured to the common bus bar 17, and with individual leads 41, 42, 43 and 44 which are secured to the respective bus bars 22, 23, 24 and 25. Electrical current supplied through bus bar 17 thus flows through the core 30 in the principal body portion 16 of the heater unit and then in series through the respective arms thereof for eventual discharge through line 45 which connects the individual leads "bus bars 56, 57 and 58 positioned adjacent the tips of the respective arms, while bus bar 51 performs a similar function with respect to the oppositely disposed portions of the unit comprising arms 60, 61 and 62 and their terminal bus bars. As indicated by the exploded representational view of FIG. 8, the core layer serving the one side of the heating unit, as indicated at 63, is insulated from the oppositely disposed core layer 64 by means of an insulation strip 65 which is preferably of the same plastic material as panels 31 and 32. Thus, when the article is pressed together to form a unitary structure as shown in FIG. 9, the article presents a uniform surface inasmuch as the material of strip 65 has been extended outwardly in some measure so as to form an even, integral bond with the panel membcrs 31 and 32.

The double bus bar structure of FIGS. 7, 8 and 9 has the advantage that it eliminates the presence of relatively unheated surfaces in the portions of the unit lying immediately above or below the bus bar. This difficulty arises since the current flow from a given bus bar which is productive of heat begins at its edge, and thus substantially no current passes through the layer of semiconductor which lies along the side of the bus bar. However, by displacing the one bar from the other in the fashion here shown, with a fully heated layer of semiconductor running along the full width of each bus bar, those surfaces of the heating unit which overlie the several centrally disposed bus bars, as at 51 and 52, are brought to the same temperatures as those which prevail at the other surfaces of the heater unit. 1

A heater unit having the shape presented in FIG. 7 is adapted to be fitted against either the interior or the exterior wall ofa sphere, as shown schematically in FIG 10.

I claim:

l. A combination ofa flexible planar heating unit and an article to be heated by said heating unit, said heating unit adapted to receive electrical current through spaced bus bars provided therein, said heating unit comprising an inner, semiconductive core layer bearing said bus bars which is laminated between electrically insulating face panels bound to said layer and to one another outwardly of the margins of the core layer about the entire periphery of the heating unit, said unit presenting, in outline, a principal body portion having a core layer provided with bus bar means and, projecting from said body portion in directions generally perpendicular to said bus bar, a plurality of spaced, generally parallel arms each containing a core layer which is integral with that inthe principal body portion and which is provided with a bus bar adjacent its outer extremity whereby current supplied to the first mentioned bus bar means passes through the core layer of the principal body portion of the heating unit and then in a parallel flow through the core layer of the projecting arms to the respective bus bars provided therein, thereby heating the heating unit, said article having a curved surface of nonsimple configuration to which is secured one face of the heating unit in good heat transfer relationship, the principal body portion and connecting arms of the heating unit being flexed to accommodate the surface of the heater to the underlying surface of the article without engendering substantial folding or overlapping of the elements of the heating unit as the latter is secured to the said article surface 2. The structure as recited in claim 1 wherein the article to which the heating unit is secured is substantially spherical in shape. I

3. The structure as recited in claim 1 wherein the surface of the article to which thehcating unit is secured is one of compound curvature configuration. 

1. A combination of a flexible planar heating unit and an article to be heated by said heating unit, said heating unit adapted to receive electrical current through spaced bus bars provided therein, said heating unit comprising an inner, semiconductive core layer bearing said bus bars which is laminated between electrically insulating face panels bound to said layer and to one another outwardly of the margins of the core layer about the entire periphery of the heating unit, said unit presenting, in outline, a principal body portion having a core layer provided with bus bar means and, projecting from said body portion in directions generally perpendicular to said bus bar, a plurality of spaced, generally parallel arms each containing a core layer which is integral with that in the principal body portion and which is provided with a bus bar adjacent its outer extremity whereby current supplied to the first mentioned bus bar means passes through the core layer of the principal body portion of the heating unit and then in a parallel flow through the core layer of the projecting arms to the respective bus bars provided therein, thereby heating the heating unit, said article having a curved surface of nonsimple configuration to which is secured one face of the heating unit in good heat transfer relationship, the principal body portion and connecting arms of the heating unit being flexed to accommodate the surface of the heater to the underlying surface of the article without engendering substantial folding or overlapping of the elements of the heating unit as the latter is secured to the said article surface.
 2. The structure as recited in claim 1 wherein the article to which the heating unit is secured is substantially spherical in shape.
 3. The structure as recited in claim 1 wherein the surface of the article to which the heating unit is secured is one of compound curvature configuration. 